The present invention relates to methods and apparatus for pneumatically transferring a flowable product from one location to another, such as transferring caustic soda beads from a railcar to a storage container.
A product such as caustic soda beads is typically transported in containers such as railcars and is transferred from the railcars by means of air streams in which the beads become entrained. It is necessary that the air streams be dry because caustic soda beads are very hygroscopic and will absorb moisture present in the air. When moisture is absorbed, a hydrate is formed on the surfaces of the beads, tending to bind the beads together into lumps which become harder as more moisture is absorbed. As a result, the beads become more difficult to transfer and are in a less desirable condition after being transferred.
One conventional unloading apparatus, depicted schematically in FIG. 3, comprises a closed-loop pneumatic circuit 1A in which pressurized air is continuously recirculated. The circuit communicates with railcar outlets 2A to draw the beads from the railcar 3A and into the air which is normally pressurized by a compressor 4A to around 15 psig. The beads become entrained in the air and are transported to a receiving silo 5A. Makeup air is introduced from a branch conduit 6A which includes a dryer 7A for demoisturizing the make-up air. A portion of the pressurized air is fed into the railcar via conduit 8A to promote discharge of the beads into the circuit 1A. Among the shortcomings of such a system is the possibility for air leaks to develop in the closed-loop circuit permitting the entry of moisture into the circulated air. As noted earlier, the presence of moisture adversely affects the ability of the air to properly transport the beads.
Furthermore, a closed-loop system conducts relatively large amounts of dust particles which must be filtered out upstream of the compressor 4A to avoid the occurrence of damage thereto. This requires that large dust filters be provided which must be cleaned or replaced on a regular basis. Otherwise, the filter surfaces can become clogged to such an extent that they will break, allowing dust particles to enter and damage the compressor.
Another known system for transporting caustic soda beads, depicted schematically in FIG. 4, employs an open loop pneumatic circuit 1B wherein ambient air is drawn through a dryer 7B by a compressor 4B which pressurizes the air to about 15 psig. A portion of the pressurized air is conducted into the railcar 3B via conduit 8B to promote exiting of the beds into the circuit 1B. After conducting the beads to the receiving zone 5B, the pressurized air is discharged to atmosphere. However, such a system requires the use of a very large, costly dryer 7B in order to properly demoisturize the air, especially during summer periods of high ambient humidity.
Another shortcoming which is characteristic of both prior art systems disclosed in connection with FIGS. 3 and 4 involves an occasional clogging of the circuit 1A, 1B by the beads as the beads tend to adhere to one another. This requires a manual opening and cleaning of the conduit which is quite burdensome and time-consuming.
A further shortcoming stems from the fact that the flow characteristics of a product such as caustic soda beads are not always consistent. Therefore, the air flow conducted to the railcar in FIGS. 3 and 4 may have to be adjusted from time to time to maintain a proper flow. This adjustment is made manually and is thus burdensome on the operating personnel, and the exact adjustment which needs to be made is not known, hence the efficiency of such a system is rarely at an optimum level during periods of higher humidity.
It has been known to demoisturize air within chemical plants by compressing ambient air to relatively high pressure, e.g., 100 psig, in a conventional compressor, whereupon a considerable amount of the moisture condenses during the pressurizing step and was drained-off. The partially demoisturized air was then further demoisturized by the use of a conventional air dryer. Dried air was withdrawn from the building to pneumatically convey caustic soda beads from railcars.
It is an object of the present invention to provide novel methods and apparatus for pneumatically transferring a product in the absence of the above-described shortcomings.